The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device having an element partitioning trench.
Nowadays, due to the high integration in semiconductor devices, technology for partitioning elements from each other in a semiconductor device has become important. In the element partitioning technology, the shallow trench isolation (STI) process has become more widely used than the local oxidation of silicon (LOCOS) process.
STI includes forming an element partitioning trench and embedding insulation material in the element partitioning trench. The embedded insulative material partitions element regions, which are located on opposite sides of the element partitioning trench, from each other.
The formation of the element partitioning trench normally includes the following operations: (a) applying a thin silicon oxide film on the surface of a silicon substrate, and applying a silicon nitride film on the silicon oxide film; (b) etching and removing the region in which the element partitioning trench is formed from the silicon nitride film; (c) etching the silicon substrate using the silicon nitride film, which is patterned, as a mask to form the element portioning trench on the silicon substrate; (d) oxidizing the surface of the element partitioning trench to form a thin oxidized film (silicon oxide film); (e) depositing a silicon film having a thickness that is greater than the sum of the depth of the element partitioning trench and the thickness of the silicon nitride film to embed the element partitioning trench with insulative material; (f) performing chemical-mechanical polishing using the silicon nitride film as a stopper to polish and flatten the upper surface of the silicon oxide film; and (g) etching and removing the silicon nitride film or the silicon oxide film from the silicon substrate. These operations are performed to form an element partitioning region.
When performing operation (b) or (c), the material of an inner wall of a manufacturing apparatus may be etched and be collected on the silicon substrate. To prevent the collected material from still remaining when performing operation (d), the surface of the silicon substrate and the insulative material deposited in the element partitioning trench are acid-washed with diluted hydrofluoric acid before performing operation (d). However, the acid-washing etches the silicon oxide film between the silicon substrate and the silicon nitride film. Such etching will now be discussed with reference to FIGS. 1A to 1D and 2.
Referring to FIG. 1A, a silicon oxide film 210 and then a silicon nitride film 211 are deposited on a silicon substrate 20. Afterwards, the silicon nitride film 211 is patterned. Referring to FIG. 1B, an element partitioning trench 202 is formed on the silicon substrate 201 using the patterned silicon nitride film 211 as a mask. Then, the silicon substrate 201 is washed with diluted hydrofluoric acid to remove metals collected on the silicon substrate. In this state, referring to FIG. 1C, the hydrofluoric acid horizontally removes part of the silicon oxide film 210, which is exposed to the element partitioning trench 202. Therefore, the silicon oxide film 210 is located horizontally inward from the opening in the silicon substrate 201 at each side of the element partitioning trench 202.
Referring to FIG. 1D, when the oxidized film 203 is formed in operation (d), stress is produced under the edges of the silicon oxide film 210. This forms protrusion regions 205, which are not oxidized, on the silicon substrate 201. As shown in FIG. 2, the protrusion regions 205 are not removed in the subsequent operations. Further, the protrusion regions 205 remain when forming a gate oxide film on the silicon substrate 201, which has the element partitioning region 204. The protrusion regions 205 may result in thinning and cause the thickness of the gate oxide film to be uneven. This would decrease the reliability of the semiconductor device.
Accordingly, horizontal extension of the silicon oxide film 210 into the element partitioning trench 202, as shown in FIG. 3A, has been proposed. However, in this case, deformed protrusion regions 205a are produced in the silicon substrate 201 subsequent to operation (d). The deformed protrusion regions 205a may result in thinning and decrease the reliability of the semiconductor device.
Even if washing is not performed with hydrofluoric acid, the etching of a semiconductor device having an element partitioning may decrease the reliability of the manufactured semiconductor device.